To transport electrical energy from an offshore facility, it is usual to use a transmission cable that can be laid on the seabed. Such a transmission cable generally has an inner bundle which comprises a number of conductors for multi-phase power transmission, and which might also enclose a data communication line. This inner bundle is screened and contained in a jacket, which in turn is protected by a number of outer layers. Usually, several of these outer layers enclose some kind of armouring, for example a close arrangement of copper or galvanized steel wires. These can form a separate layer between sheaths and/or can be embedded in a sheath. An outermost armouring layer of the transmission cable serves to protect the inner layers from damage and corrosion, and is generally made of a resilient material such as a thermoset polymer, nylon, bitumen etc. The outermost armouring layer can also comprise embedded wires. To ensure that the complete transmission cable is to some extent flexible, and to increase the resilience of the armouring, any wires embedded in an armouring layer are generally arranged at a pitch angle to the longitudinal axis of the cable. The armouring wires therefore describe helical paths about the longitudinal cable axis. Different armouring layers of a transmission cable may have different and/or opposing pitch angles.
When installing an offshore facility such as a wind turbine or oil rig, a transmission cable is brought to the offshore facility by means of a pipelay vessel, and one end of the transmission cable is raised to the level of a transition platform or transition piece of the offshore facility. In the example of a wind turbine, electrical connections must be made between the wind turbine generator and the transmission cable in order to transport electrical power from the wind turbine to a grid. Similarly, electrical connections must be made between any control units of the wind turbine and a communication cable of the transmission cable. Before making such electrical connections, the conductors and any communication cable inside the inner jacket of the transmission cable must be exposed. To this end, the armouring layers must be completely removed over a certain length of the transmission cable.
At present, the step of removing the armouring layers is usually performed manually. A suitable cutting tool is used to make incisions into the outer layers of the transmission cable to a suitable depth. It is important not to insert the cutting tool too far into the armouring, otherwise the inner layers may sustain damage. Equally, it is important to make sufficiently deep incisions, otherwise the cutting step must be repeated, thereby increasing the risk of cutting too deeply. However, the material strength of the outer layers and the armouring can make it difficult to operate the cutting tools with the necessary degree of precision. Another problem arises from the difficulty of handling the heavy and unwieldy transmission cable in a confined space such as the transition piece of an offshore wind turbine. For these reasons, the step of manually removing armouring from transmission cables is presently a hazardous and costly procedure.